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e (RECEIVER) MREcEIvER) a (TRANSMITTER) j FF605 DMDER RESEHNOR 606,624)HIlHlHIIIIHHHHHHHIIllHIllIH FF 5l6 rrsaz United States Patent 3,396,322STEPPING MOTOR DRIVE CIRCUIT INCLUDING DAMPING MEANS George T.Shimahukuro, Monterey Park, Calif., assignor to Xerox Corporation,Rochester, N.Y., a corporation of New York Filed Oct. 1, 1965, Ser. No.492,221 4 Claims. (Cl. 318138) This invention relates to facsimileequipment and more particularly to facsimile transceivers adapted tooperate through the direct distance dialing telephone network eitherwith or without direct electrical connection thereto.

Facsimile transmission is old in the art. In the past, it has mostlybeen used for transmitting photographic type of information overpredetermined leased transmission channels. More recently, equipment hasbeen marketed for the high speed transmission of documents over broadband transmission channels. The present invention is particularlyconcerned with the economical and flexible transmission of letters,drawings and other black-white documents over ordinary voice gradetelephone channels.

The equipment meeting these goals should be inexpensive and theinvention accordingly, provides a facsimile transceiver wherein many ofthe components are shared between the transmitting and receivingfunction, instead of a separate transmitter and receiver.

It is desirable that the equipment be capable of transmitting documentsany location where telephones are available. The invention provides afacsimile transceiver which is capable of either transmitting orreceiving documents through any conventional telephone set withoutrequiring an electrical connection thereto. The invention provides afacsimile transceiver capable of establishing synchronism with a liketransceiver at a remote location independently of the character,frequency, or phase of the power line to which each may be connected.

The equipment should minimize the telephone charges associated with thetransmission of the document. The invention provides equipment whichdoes not require the operator to lease a so-called data set from thetelephone company, which transmits documents in a shorter time than hasheretofore been possible, and which permits the equipment operators ateach end of the transmission link to terminate the telephone connectionas soon as the connection is no longer actually needed or whenevertransmission becomes unintelligible.

The equipment should also be capable of operating through telephonecompany data sets where available, to take advantage of their improvedtransmission capability. The invention provides a facsimile transceiverwhich operates with two level signals which will interface with aconventional data set intended for the transmission of digital signalsthrough telephone lines.

The equipment should function reliably without regard to the skill ofthe operator. The invention provides a facsimile transceiver whichrequires only the insertion of a piece of paper and the dialing of atelephone call in order to provide high quality facsimile transmission.

Specific objectives will become apparent in connection with a moredetailed description of the invention and the drawings related thereto.

FIGURE 1 is an exterior view of a facsimile transceiver according to theinvention.

FIGURE 2 is a block diagram illustrating the functions of the invention.

FIGURE 3 is a simplified isometric view of the recording mechanism.

FIGURE 4 is a simplified isometric view of the transmitting mechanism.

FIGURES 5A-5E illustrate logical circuit elements used in the subsequentfigures.

3,396,322 Patented Aug. 6, 1968 "ice FIGURE 6 shows the basic timingcircuit.

FIGURE 7 shows the repetitive waveforms corresponding to FIGURE 6.

FIGURE 8 shows the transmitter and telephone transducer controls.

FIGURE 9 shows the transmitter logical circuitry.

FIGURE 10 shows waveforms generated in the circuit of FIGURE 9.

FIGURE 11 shows a video amplifier circuit used in FIGURES 9 and 10.

FIGURE 12 shows the printer power and control circuits.

FIGURE 13 shows an alternate form of FIGURE 12.

FIGURE 14 shows the stepping motor drive amplifier.

FIGURE 15 shows the printer logical circuits.

FIGURE 16 shows waveforms illustrating the achievement ofsynchronization.

FIGURE 1 shows the external appearance of a form of facsimiletransceiver according to the invention. The apparatus is enclosed by acabinet including a generally horizontal aperture 121 in its forwardlyfacing surface. Visible within the aperture is a rotatable drum 122including a clamp bar 123. Aperture 121 permits access to the drum sothat an operator may fasten a sheet of paper to the drum to make afacsimile recording thereon. On top of the cabinet is a tray 124 forholding a document to be transmitted and feeding it through a slot 125into the scanner mechanism 126. Cabinet 120 also includes a reset buttonand an indicator light 131. Adjacent to the cabinet 120 and connectedthereto is a box 127 which is adapted to contain a standard telephonehand set and is provided with a hinged cover 128 and latch 129.

FIGURE 2 is a schematic diagram showing, in general terms, how two ofthe facsimile transceivers of FIGURE 1, each at a different location,may be interconnected to form a bidirectional facsimile system. Itshould be understood however, that the functional blocks shown in FIG-URE 2 correspond in only a very general way to the circuits or circuitfunctions described in subsequent figures. The first step in sending adocument is for the operator at one location to use his telephone todial the corresponding telephone 135 at the other location, generallythrough one or more intervening telephone exchanges 136. After a normalvoice connection has been confirmed by the operator at each piece ofequipment, each operator places his handset 137 in box 127 and closesthe cover. Either operator inserts a document through slot 125 into thescanner 126 of his unit. Scanner 126 then sends a control signal totransmit/receive circuit which, responsive to the document in scanner126 and the handset in box 127, adapts the transceiver to the transmitmode. Scanner 126 also sends video signals to transmitter 138 whichprocesses the signals and uses them to control the operation of scanner126. Meanwhile, transmitter 138 combines the video signals with controlsignals from transmit/receive circuit 140 and introduces them intohandset 137 from which they are transmitted over the telephone line. Atthe same time, even though transmitting is taking place, timing andpower circuit 139 is exchanging signals with printer 142 and generatingfurther signals for processing by transmit/ receive circuit 140.

At the other transceiver a signal is picked up from the correspondinghandset 137 and detected by receiver 141 which causes transmit/ receivecircuit 140 to put the transceiver into the receive :mode. The receivedsignals also cause transmit/receive circuit 140 to control the operationof timing and power circuit 139 so as to bring printer 142 intosynchronism with scanner 126 of the transmitting transceiver. Thereceived signals are applied to printer 142 and cause it to record afacsimile of the transmitted document.

At each transceiver a supervisory circuit 143- monitors the operation ofthe various circuits so that a corresponding alarm sounds at each of thetwo transceivers when a transmission is either completed or interrupted.The alarm signals each of the two operators to lift up their handsetsand talk to each other to determine whether documents are to beretransmitted, more documents are to be transmitted in either direction,or whether the telephone connection should be terminated.

It is obvious from the preceding description that an unlimited number offacsimile transceivers according to the invention may be used inconnection with each other, since any one can be functionally connectedwith any other, for either transmitting or receiving, through theconventional switching facilities of the telephone companies. Conferencecall arrangements may also be used to permit one transceiver tosimultaneously transmit to a number of others.

FIGURE 3 is a simplified isometric view of the printing or recordingmechanism. Drum 122 is journaled for rotation in bearings, not shown,and is driven through gears 151, 152 and 153 by motor which ispreferably, although not necessarily a two pole synchronous motor withmeans, for example a permanent magnet rotor for providing a predictablerelationship between electrical power phase and rotational phase. Motor150 bears a pinion 151 which drives idler gear 152 at a 2 to 1 reductionratio, and idler gear 152 drives drum gear 153 at a 10 to 1 reductionratio. Attached to drum 122 are a pair of cams 162 and 163 which actuateswitches 164 and 165 respectively. The functions of these switches willbe described subsequently in connection with a description of FIGURES 6and 12. A pen carriage 154 is located adjacent to drum 122 and slideablymounted on rails 155 which are parallel to each other and to drum 122.The pen carriage 154 carries a marking tip 156 which may be urged intocontact with the drum by an electromagnetic assembly 1157 and urged awayfrom the drum by spring 158. A flexible electrical cable 166 carriescontrol voltages to the electromagnet assembly 157 and to marking tip156 itself. The pen carriage 154 also engages a lead screw 159 which isincrementally driven by either a forward stepping motor 160 or reversestepping motor 161, the two stepping motors being connected to eachother and to the lead screw. In this manner, marking tip 156 can beadvanced in uniform discrete increments on the order of 0.01 inch in adirection parallel to the axis of the drum in response to commandsderived from circuitry which will be described later on.

Marking tip 156 may take many different forms as is known in the art. Itmay comprise an electrically insulated metal stylus adapted to writedirectly upon conventional electrolytic facsimile recording paper. Thesame form of stylus can be used to deposit electrostatic charge on aninsulating sheet for subsequent development by known Xerographictechniques. A simple metal stylus can also be used to record directly onpressure sensitive recording paper through selective energization ofelectromagnet assembly 157. Various forms of apparatus for the selectivedeposition of liquid ink may be employed. A variable intensity focusedlight source may also be employed for forming a latent image on a sheetof photographic paper or the like. Any of these methods or any othersuitable facsimile recording technique may be employed with theinvention.

FIGURE 4 is a simplified isometric view of a form of scanning mechanism126. A pair of drive rolls 176 is provided with cog wheels 177, as is astepping motor 178 which may be identical with motor 160 or 161 of FIG-URE 3. Motor 178 incrementally drives rolls 176 through a so-calledtiming or cogged belt 179. Each drive roll 176 cooperates with a pinchroller 180 immediately above it to feed a sheet of paper through thescanner in increments on the order of 0.01 inch. Fluorescent lamps 181,preferably operated by direct current, are positioned beneath driverolls 176 and are provided with reflectors, not

shown in this figure, to direct light upwardly against the lower surfaceof a sheet of paper passing through the rolls, and supported on aslit-containing platen, also not shown in this figure. A mirrorgalvanometer 183, including a small mirror, 184, samples light reflectedfrom the sheet of paper and passes it through lens 185 tophotomultiplier 186 or other photosensitive device. Since the mirrorgalvanometer is a device adapted to rotationally oscillate the mirrorabout an axis, the photomultiplier 186 is enabled to scan a samplingspot back and forth in a line across a document or other sheet of paperpassing through the drive rolls.

FIGURE 5 illustrates certain forms of elementary logic circuits whichare widely used in subsequent figures of this specification. FIGURE 5Ashows the NAND and NOR gate symbols and a suitable transistor circuitfor realizing the function represented by the symbols. The illustratedNAND and NOR symbols actually denote the same circuit function, asshown, for example, in MILSTD-8-06B, Feb. 26, 1962. In terms of theillustrated transistor circuit, the symbols represent the followingfunction: the output voltage is minus 6 volts if, and only if, allinputs are at zero volts, otherwise the output is at zero volts. It isconvenient to regard most of the gates in later figures as NAND gateswith 1 equal to zero volts and 0 equal to minus 6 volts. FIGURE 5B showshow two of the circuits of FIGURE 5A can be cross-coupled to provide aflip-flop circuit. The flip-flop is characterized in that it will changestate only when an input voltage of minus 6 volts is applied to theappropriate input terminal. Specifically, if minus 6 volts is applied tothe Reset input, then the flip-flop will be Set, i.e., the 1 output willbe at zero volts and the 0" output will be at minus 6 volts. FIGURE 5Cshows an obvious and self-explanatory modification of FIGURE 5B in whichthe flip-flop can be set to one of its states by a voltage of minus 6volts applied to either of two corresponding inputs. FIGURE 5D shows howan inverter function is provided by the logic gate of FIG. 5A. FIGURE 5Bshows a trigger flip-flop which changes state as a result of a pulseapplied to the single input terminal. In the form used in thisspecification, the input signal is a six volt positive going pulse andthe output voltages are either zero or minus 6 volts. The illustratedtransistor embodiments of the described circuit functions can beobtained in module form from the Engineered Electronics Company of SantaAna, Calif. The NAND/NOR circuit is their model Q-411 or Q-42l and thecircuit of 5B represents two models Q-412 or Q-422.

The symbols and circuits of FIGURE 5 represent those chosen for use inthe illustrative embodiment of the invention. The functions representedby the logic symbols can be realized by circuits of many formsobtainable from numerous manufacturers and all of which are well knownin the art. Those skilled in the art will also realize that logicalcircuitry of the type to be shown in subsequent figures has a certainoverall input-output relation which can be duplicated using diiferentarrangements of the same basic logical elements and furthermore, thatthis function can be realized using quite different types of logicelements which need not even be electronic. Merely as an illustration itmay be noted that AND/OR gates may be substituted for the illustratedNAND/OR gates and that it might even be possible thereby to simplify thedescribed embodiment of the invention. In general, the designer willchoose the type and design of his logical building blocks based on suchconsiderations as cost, size, reliability, voltage and currentrequirements, speed, fan-in and fan-out capabilities, etc.

Timing circuits FIGURE 6 shows the timing circuits used to generate thetiming waveforms shown in FIGURE 7, which are used in controlling theoperation of the facsimile transceiver. A tuning fork or other stableoscillator 201 provides a 3840 cycle output frequency which is processedby pulse shaping circuit 202 to provide a train of positivegoing pulsesat the oscillator frequency. These pulses are applied to a counter ordivider chain of seven sequentially connected trigger flip-flopsidentified as I through VII. A higher frequency crystal oscillator withadditional dividers may also be employed. For convenience the first sixstages only are regarded as constituting a distinct scale of 64 counter203 and are so shown in the figure. Each counter can be simultaneouslyreset to zero from a common source through coupling diodes 204, but thereset function will not be described except in connection with FIGURE15. The output of stage VI is a 60-cycle square wave identified assignal A which is used to drive motor 150 as shown in FIGURE 3, l2 and13. The output of stage VII is a 30-cycle square wave H. Motor 150rotates at 3600 r.p.m. and drives drum 122 at 180 r.p.m. so that onerevolution requires 333 /3 milliseconds or 20 cycles of signal A. Drum122, acting through cams 162 and 163 and switches 164 and 165 generatestiming signals M, M and S in a manner which will be more fully shown inFIGURE 12. In terms of the rotation of drum 122, signal M is in the zerovolt or logical 1 state from 355.5 to 7.5 and S is in the 1 state from22 to 36. Signal M is simply the inverse of signal M. For reasons whichwill become apparent later, the otherwise arbitrary zero degree positionof drum 122 should be chosen at a point where marking tip 156 is overclamp bar 123. Because of the fixed relationship existing betweenfrequency divider 203 and drum 122 it is convenient to use the angularposition of drum 122 for specifying the various waveforms generated inFIGURE 6. For convenience it may be noted that in the illustratedembodiment one cycle of oscillator 201 corresponds to .26 millisecondsand also corresponds to .28 of rotation of drum 122. Thus, one degree ofrotation corresponds to about .93 milliseconds.

The 0 outputs of stages III and IV of counter 203 are combined in NANDgate 205, the output of which is inverted by inverter 210, delayedslightly by capacitor 224 and applied to AND gate 215. This signal is inthe logical 1 state whenever counter 203 is at counts 0 to 3, 16 to 19,32 to 35, or 48 to 51. Further processing of this signal will bedescribed later.

The 0 outputs of stages V and VI of the counter are combined in AND gate206 and the resulting signal inverted to provide signal D which is inthe logical 1 state whenever divider 203 registers counts zero throughfifteen, inclusive. This output, accordingly, appears 20 times perrevolution at 0 to 4.5"; 18 to 22.5; 36 to 40.5, etc. and is referred toas the advance clock signal.

The 0 output of stage V is combined with the 1 output of stage VI ingate 207, the output of which is inverted in inverter 212 to provide asignal which is at the logical 1 level during counts 32 to 47 inclusive.This signal is combined in NAND gate 217 with incoming signal S which isat the 1 level from 22 to 36. The output of gate 217, inverted byinverter 228, is a signal which is at the logical 1 level from 27 to31.5 only and is identified as the prevideo signal G.

' 18; 31.5 to 36 etc. and is used internally as an input to gates 218,220, 221, 222 and 223. The other input to gate 218 is the 1 input ofstage IV. Accordingly, the output of gate 18 is the triple coincidenceof counter stages IV, V, V2. This is inverted in inverter 229 to providea signal which is at the logical 1 level for counts 50 to 63 inclusiveor 15% to 18; 33% to 36; 51% to 54, etc.

The triple coincidence of the 1 output of stages IV, V, VI is alsodetected in gate 209, inverted in inverter 214, combined in gate 219with the 1 outputs of stages II and III and finally, inverted ininverter 230. The resulting signal is accordingly at the logical 1 levelfor counts 62 through 63 inclusive. This signal is identified as L andappears from 359.4 to 360; 176 to 18; 356 to 36 etc.

The output of inverter 213 is also combined in gate 220 with signal S toproduce a minus 6 volt output pulse extending from 315 to 36. This pulseis applied to one input of fiip-fiop 231. The output of inverter 213 isalso combined in gate 221 with signal M to produce a minus 6 volt signalextending from 355.5 to 0. This pulse is applied to the other input offlip-flop 231. Inasmuch as the flip-flop is alternately set and reset bythe signals appearing at its two input terminals, a signal at theappropriate output terminal will be at the logical one level from 31.5to 355.5. This signal is designated as video gate signal J. The outputof gate 221 is also inverted in inverter 132 to form a signal which isat the logical 1 level from 355.5 to 0 and which is referred to as videoend signal E.

The output of inverter 213 is also applied to the first inputs of NANDgates 222 and 223, the outputs of which are connected to opposite inputterminals of a fiip-fiop 233. The second input of gate 222 is connectedto the signal M while the second input of gate 223 is connected to theinverse of signal M, namely M. Thus, flip-flop 233 changes state everytime signal M changes state, but the change is delayed in each instanceuntil a logical 1 signal is received from inverter 213. Accordingly,flipflop 233 changes state at 355.5 and 135, rather than at 352.5 and7.5 The output of flip-flop 233, extending from 355.5 to 13.5 isdesignated signal N.

Returning to the previously described signal D, this signal is combinedin gate 216 with signal M which acts as a window to permit only one Dsignal per revolution to pass through The resulting signal is invertedby inverter 127 and constitutes a signal B, which is at the logical 1level from 0 to 4.5 only. The output of gate 216 is also applied to adelay multivibrator circuit 125 which delays it for nearly a fullrevolution of drum 122 to provide the signal Q shown in FIGURE 7.

Signal B is also combined in gate 215 with the previously describedoutput of inverter 210'. The negative output of gate 215 thus extendsonly from counts 0 to 3 of counter 203 and only at the zero degreeposition of drum 122. The resulting signal is inverted in inverter 126to produce a signal designated C which is at the logical 1 level from 0to 113 only.

FIGURE 7 shows the above-described waveforms plus a synthesized waveformm which is the coincidence of the previously described F signal and theinverse of the described D signal. This composite signal extends from 45to l3.5; 225 to 315 etc. This particular waveform will be used inconnection with FIGURE 9 together with certain other illustratedwaveforms.

Transmitting circuits FIGURE 8 shows the scanner and telephoneassemblies schematically in somewhat greater detail, together with theirassociated circuitry. It can be seen that the fluorescent la-mps 181,shown previously in FIGURE 4, are provided with reflectors 301 and thata. platen 302 is provided to support a document face down as it passesthrough the drive and pinch rolls 176 and 180. A slit 303 is provided inthe platen between the lamps and immediately over the mirrorgalvanometer 183. Also shown in this figure is an aperture or stop 304which is positioned between lens and photomultiplier 186 to limit anddefine the size of the sampling area which is scanned back and forthacross the document by mirror galvanometer 183.

Mirror galvanometer 183 may be any suitable device capable of rapidlyconverting an input signal into a corresponding rotation of a mirror.Commercially available mirror galvanometers of the type sold for use inmultichannel optical recording 'oscillographs represent a suitabledevice of this type. A particularly suitable device for use in theillustrated embodiment of the invention can also be made by cementing aone-half inch diameter mirror to the pen shaft of a pen recordinggalvanometer, catalog No. 428647920138, manufactured by The BrushInstruments Division of the Clevite Corporation, or to the shaft ofcomparable devices made by the Sanborn Division of Hewlett-PackardCompany.

Also shown in this figure are paper detector switches 306 and 307 whichare positioned to detect the presence of a sheet of paper in thescanner. Switch 306 detects the presence of a sheet of paper as it isfirst presented to the scanner on the left side thereof, and switch 307detects the presence of a sheet of paper within the scanner andapproximately at the position of slit 303. Switch 306 operates anassociated multicontact relay K1 and switch 307 operates an associatedmulticontact relay K2. Switch 307 may be replaced by a time delaycircuit actuated by switch 306, Operating power for these relays passesthrough a switch 308 which is located in telephone box 127, and which ispositioned so that it will close and pass current to relays K1 and K2only if a telephone handset is properly seated in the box. Only ifswitch 308 is properly closed will insertion of a piece of paper intothe scanner enable switch 306 to operate relay K1. Among its otherfunctions, relay K1 transfers a contact Kla which supplies minus 6 voltsto a resistor 312, the other end of which is grounded. The voltageappearing across resistor 312 is supplied to inverter 313, the output ofwhich is a transmitter control voltage T which is at the logical 1 levelonly when relay K1 is operated. This output T is used to control theoperation of the transceiver in the transmit mode. When switch 308 isclosed but relay K1 is not energized, minus 6 volts is applied toresistor 322 instead of resistor 312. The voltage appearing acrossresistor 322 is supplied to inverter 323, the output of which is at thelogical 1 level only when switch 308 is closed and relay K1 is notenergized and, therefore, provides a receiver control voltage R tocontrol the operation of the transceiver in the receive mode. Relay K2has a contact a which holds relay K1 closed as long as relay K2 isclosed. Accordingly, relay K1 will remain closed as long as a documentis still over slit 303 and signal T will remain at the logical 1 levelfor that time. Relays K1 and K2 and other relays to be described laterare shown with their contacts in the de-energized state of the relay.The relay contacts are not necessarily shown in physical proximity tothe relay coil symbol.

Drive motor 178 is shown in association with a pair of drive coils 305.Many types of stepping motors may be used for motor 178, or motors 160and 161. They may be, for example, an ordinary electrical solenoidassociated with a pawl and ratchet drive, a rotary solenoid associatedwith a one-way drive clutch, a driving mechanism of a conventionalstepping relay, or the so-called Cyclonome stepping motor sold by SigmaInstruments, Inc. This latter type is preferred and, as is well known,incorporates a pair of driving coils, corresponding to referencecharacter 305, which are energized alternately by means to be shown inFIGURE 14.

Photomultiplier 186 is connected to a gated squaring amplifier 321, morefully illustrated in FIGURE 11.

The energization of galvanometer 183 is controlled by a contact'b ofrelay K2 so that the galvanometer is enabled to operate whenever adocument is in position above the slit 303. The galvanometer drive powercomes from either a prescan generator 319 or a scan generator 320, underthe control of relay K6, which is under the control of the circuits ofFIGURE 9. Scan generator 320 provides a linear ramp voltage which issynchronized with the rotation of drum 122 by means of incoming signal Tfrom FIG. 6. Prescan generator 319 filters and amplifies the incoming30-cycle square wave H from FIG. 6 to provide a 30-cycle sine wavesignal which has ten cycles or twenty half-cycles per revolution of drum122. A triangular wave would also be suitable. Suitable circuits forgenerators 319 and 320 are to be found in 'FIG- URES 7 and 8,respectively, of SN. 471,799, filed July 14, 1965. The reasons forproviding both a high speed and a low speed scanning waveform willbecome apparent later in the specification and are also set forth insaid SN. 471,799, filed July 14, 1965.

Referring to telephone box 127, there is provided a small loudspeaker309 and a soft annular gasket 310 to seal the loudspeaker 309 to themicrophone unit of handset 137. Loudspeaker 309 is connected through arelay K4 to modulator 314. Relay K4 is operated by switch 308 so as toconnect the modulator to the loudspeaker only when the transceiver is inthe transmitting mode. The modulator may be of any of the varietiesknown to the art. A highly satisfactory form of modulator comprises avoltage controlled multivibrator oscillator followed by an audioamplifier, such that sound at 1300 cycles is applied to the telephonefor one of the levels of a two-level input signal applied to themodulator, and sound of about 2300 cycles for the other input level.This arrangement has proven very satisfactory for introducing facsimilesignals into a telephone circuit without making an electrical connectionthereto. When the transceiver is not in the transmit mode, loudspeaker309 is disconnected from modulator 314 and is connected through relay K4to an alarm tone generator 315 which is controlled from the alarmcircuits of FIGURE 13 and supplies a lower frequency sound, i.e., 800cycles, into the telephone.

An inductive pickup coil 311 is provided in telephone box 127 under theearphone end of handset 137 to pick up incoming signals. The coil may beof the shape shown and may be comprised, for example of 7900 turns of#34 insulated wire with an inductance of about 2.2 henries at 1000cycles. It has been found that there is sufi'icient leakage flux from atelephone receiver, particularly those used in the Western Electric 500subscriber set, to permit efficient signal pickup my means of theillustrated coil. As an alternative, particularly where the facsimileequipment must be used with other types of telephone instruments havingwell shielded receivers, pickup coil 311 may be replaced by a microphoneacoustically coupled to handset 137 for picking up the acoustic signalsradiated by the handset. These signals from coil 311, or from themicrophone, are demodulated in a demodulator 316 of a type appropriatefor use with the selected form of modulator 314 to produce an outputsignal corresponding to the input signal to modulator 314. If desired,Coil 311 can also be used to couple signals into a telephone fortransmission. A terminal 317 is also provided on the output side ofdemodulator 316 to permit the direct re ception of facsimile signalsfrom a telephone company data set or the like, as an alternative tosignal transmission via a conventional telephone subscriber set, asshown in FIGURE 8. A very sharply tuned, narrow band demodulator 318 isalso connected to pickup coil 311 to provide an output signal responsiveto detection of a selected tone transmitted by alarm tone generator 315.

Voice grade telephone lines are a convenient facsimile transmissionmedium because of their universal availability, but provide a far fromideal transmission medium for facsimile or other data type signals. Forthis reason, it is desirable in modulator 314 and demodulator 316 toprovide the technical refinements which are known to the art, in orderto maximize the quality of transmitted images and the speed at whichthey can be transmitted. While not a part of this invention, it has beenfound desirable to pass the facsimile signals intended for transmissionthrough a low pass filter to eliminate abrupt transitions and shift thesignal power spectrum toward lower frequencies and to apply thisfiltered signal to an FM or frequency shift (FSK) oscillator, such as aVoltage controlled multivibrator, which has linear output frequencyversus input signal characteristics. At demodulator 316, it is desirableto employ delay equalization to compensate for the non-uniform delayversus frequency characteristics of a typical telephone channel, and toapply the resulting phase delay compensated srgnal to a wide bandfrequency modulation or frequency shlft detector to derive a suitableoutput signal. With these refinements it is possible to achieve highquality facsmnle transmission, making effective use of the nationalswitched telephone network, even allowing for the inevitable signaldegradation involved in transducing the facslmrle output signal througha loudspeaker into the carbon rnrcrophone of a telephone and intransducing the input signal from an imperfect telephone receiver. Otherforms of modulation, such as amplitude modulation or vestigial sidebandmodulation may also be employed.

FIGURE 9 shows the logical circuitry which is used to control theoperation of the facsimile scanner and to generate an appropriatefacsimile signal for transmission. As an aid in understanding theoperation of the illustrated circuits, the paths of the principaltransmitted signals, as opposed to internal control signals, are shownin bold lines. There are four of these signals which are combined in afour input NOR gate consisting of gates 402 and 405, gated against thetransmit control signal in gate 406, and applied to the modulator 314,previously described in connection with FIGURE 8. A terminal 422 is alsoprovided to permit these signals to be applied directly to a data set.The first of these signals is the facsimile video sign-a1 itself, whichis a two-level signal derived by amplifier 321 from the output ofphotomultiplier 186 which is, in turn, related point by point to thedensity of a document being scanned with the aid of mirror galvanometer183. This signal is gated in NAND gates 401 and 404. One of these gatingsignals is the signal I which prevents the video signal from evergetting through to NOR gate 402 in the interval from 355.5" to 315 ofthe drum rotation of drum 122, this period being allotted to thescanning of clamp bar 123 and for the transmission of certain controlsignal. The next slgnal of significance is the previously described onceper revolution prevideo signal G which is gated in NAND gate 416 by anoutput of advance control flip-flop 414. The third signal is the 20times per revolution advance clock signal D which is gated on and off inNAND gate 418 by the other output of flip-flop 414 from that used tocontrol the prevideo signal in gate 416. The fourth signal is E which isa one time per revolution signal and the inverse of the previouslydescribed B signal. This signal, unlike the others, is applied directlyto the NOR gates 402 and 405 without inversion in a prior NAND gate.This signal must pass through a normally open contact of relay K1 and anormally closed contact of relay K2.

In addition to generating a composite video signal for transmission, thecircuit of FIGURE 9 generates two other important signals for internaluse. One of these signals is a composite of the D and B signals only,from the transmitted video signal. This signal is generated by means ofa NAND gate 419 which has the same input connections as NAND gate 405,and the output of which is gated in NAND gate 420 by the transmitcontrol signal, in the same manner as the composite video signal isgated by gate 406. This signal is applied, through circuits shown inFIGURE 12, to the scanner stepping motor 178, shown in FIGURE 8. Later,it will be shown that this component of the transmitted video signalcauses pen carriage 154 at a remote connected transceiver to advanceincremently in synchronism with the document advance in the transmittingtransceiver. The other signal produced in FIGURE 9 is the output of scancontrol flip-flop 410 which is applied to relay K6 in FIGURE 8 tocontrol the operation of mirror galvanometer 183 between the slow,one-linear scan per revolution mode, and the fast scan mode in whichtwenty back and forth scans are made per revolution.

The circuit of FIGURE 9 commences to function when a telephone is placedin box 127 of FIGURE 8 and a document is inserted into the scanneractuating switch 306, also of FIGURE 8. This will energize relay K1, closing contact Kla in FIGURE 9 and permitting signal B to pass throughnormally closed contact K20 and through gates 405 and 406 fortransmission to a remote transceiver. This same signal is alsotransmitted through gates 419 and 420 to the apparatus of FIGURE 12 fromwhich it returns to stepping motor 178 of FIGURE 8 to operate the motorat a rate of 1 incremental advance per revolution of drum 122, i.e.three advances per second. The transmitted signal under the describedconditlons is shown in FIGURE 10a. When a document has advanced to theposition of switch 309, relay K2 will be energized thus opening normallyclosed contact K20 and lnterrupting the transmission of the B signals.At the same time, contact K212 (FIGURE 8) will close and iggimence thescanning operation of mirror galvanometer At this point, it is necessaryto consider the signals emanating from photomultiplier amplifier 321 aswell as the initial states of control flip-flops 408, 410, 414 and 417.Assuming that the apparatus is to be adapted for use with ordinarydocuments having black on white informatron, rather than the reverse,the output of amplifier 321 Wlll be at the logical 1 level, i.e., zerovolts, when the photomultiplier is looking at a black element of thedocument and at the logical 0 level, i.e., minus 6 volts, when thephotomultiplier is looking at a white background element. Initially,i.e., before photomultiplier 186 sees any printed material or the like,flip-flops 408, 410, 414 and 417 will be in the l, 0, 1, and 1 states,respectively. This can be verified by examining a subsequent discussionof the operation of the circuit when photomultiplier 186 scanscompletely blank lines on the document after having scanned linescontaining marks, printing or the like. Under the initial conditions,flip flop 410 acting through gate 404 prevents any signals fromamplifier 321 from being transmitted and also leaves relay K6 in FIGURE8 deenergized so that galvanometer 183 is connected to prescan generator319. Flip-flop 414 enables D signals to pass through gate 418 and to betransmitted through gates 405 and 406. This same signal is alsotransmitted through gates 419 and 420 to operate stepping motor 178 inFIG- URE 8. Finally, flip-flop 414 also disables gate 416 and preventsprevideo signal G from being transmitted. The transmitted signal underthe described condition is shown in FIGURE 1012. Under these conditions,the transmitted document is advanced at the rate of 60 increments persecond, which is 20 times as fast as lines can be recorded on drum 122.As will be shown later, pen carriage 154 is advanced at this same rapidrate in a remotely con nected matching transceiver.

As soon as a black area is detected in the document being scanned, theoperation of the circuit of FIGURE 9 becomes quite different. Theabsence or reduction of light falling on photomultiplier 186 causes alogical 1 output signal to be produced by squaring amplifier 321 andthis signal is enabled to pass through gate 403 to set flip-flop 408 tothe 0 state and thereby reset flip-flop 410 to the 1 state. The newstate of flip-flop 410 causes galvanometer 103 to be connected to theslow scan generator 320 rather than the fast prescan generator. At thenext coincidence of the D and F signals (see FIGURE 7) the logical 1level at the 0 output of flip-flop 408 is enabled to pass through gate411 to set flip-flop 414 to the 0 state, thereby preventing any furtheradvance clock signals D from passing through gate 418, but permittingthe next D signal to set flip-flop 408 to the 1 state through gate 407.No further signals are transmitted until the next appearance of prevideosignal G. The transmitted signals during a drum revolution of this typeare shown in FIGURE 100. At the next appearance of the prevideo signal Gthe level at the output of flip-flop 414 is enabled to pass through gate416 to set flip-flop 417 to the 0 condition and at the same time the Gsignal is applied to NOR gate 402 and passes through gate 406 fortransmission. The 0 output of flip-flop 417 is applied to gate 404 anddirectly thereafter (see FIGURE 7) video gate signal I is applied togate 401. The combined presence at gates 401 and 404 of signal I, the 0output of flip-flop 417, and the 1 output of flip-flop 410 enables thevideo signals from amplifier 321 to pass through gates 401 and 404 andthrough gate 406 for transmission. The remainder of this revolution, orslow scan cycle, is given over to the transmission of video informationdetected by photomultiplier 186, as shown in FIGURE d. It should benoted that the line now being scanned by galvanometer 183 is the sameline .which was scanned once before at a more rapid rate under controlof prescan generator 319, since the initial and immediate effect of thedetection of a black area in the transmitted document was to prevent anyfurther advance clock pulses D from either being transmitted to a remotetransceiver or from being applied to stepping motor 178.

At the end of a slow scan of the type shown in FIG- URE 1011, the videoend signal E passes through gate 415 and sets flip-flop 414 to the 1condition, whereby the next advance clock signal D is enabled to passthrough gate 418. At the same time, 6 sets flip-flop 417 to the 1 stateand short master signal C is enabled to pass through gate 409 to resetflip-flop 410 to the 0 state and once again enable video signals fromsquaring amplifier 321 to reach flip-flop 408. Galvanometer 183 is nowagain connected to prescan generator 319 which is phased with rsepect tothe slow scan generator 320 so as to provide a rapid retrace followingthe slow scan. If no black areas are detected in the document beingtransmitted during this retrace interval, the galvanometer will continueto be driven by the fast prescan generator 319 and advance clock signalD will be transmitted through gate 418 after each fast scan. Thetransmitted waveform will then be as shown in FIGURE 10d. However, assoon as a black area is detected, the circuit of FIGURE 9 will revert tothe slow scan mode already described and the transmitted signal for theremainder of the slow scan cycle will be as in FIGURE 10c. If a blackarea is detected along the very next scan line the transmitted waveformwill be as in FIGURE 10a.

The operation of the facsimile transceiver in the transmit mode can nowbe described in a simpler way. In the absence of black areas or othermarks which the photomultiplier and amplifier are designed to detect, adocument will be rapidly scanned alternately from left to right and fromright to left. No video information will be transmitted in thiscondition but characteristic advance signals will be transmitted andwill also be directed to the transmitter stepping motor to advance adocument one increment at the end of each scan. If a black area isdetected during a fast scan, then the document is not advanced anyfurther, a document advance signal is not transmitted, and the scanningaction reverts to the slow mode. When the scanning mechanism, i.e.,galvanometer 183, reaches the time and position at which a slow scan isabout to commence, a characteristic prevideo alerting signal istransmitted and thereafter video signals corresponding to the scan aretransmitted. At the end of the slow scan the document is advanced oneincrement, a paper advance signal is transmitted, and the galvanometerexecutes a rapid retrace during which video signals are not transmitted.If information is detected during the retrace, then a further slow scanis made and further paper advances or advance signals are withheld untilthe end of the slow scan. If no information is detected during the fastscan retrace, then the document is advanced at the end of the retrace,an advanced signal is transmitted, and further rapid scans and advancesare made until such time as black areas or other information aredetected. In this way, every elemental line of the document whichcontains information is scanned twice, first with a rapid scan and thenwith a slow scan during which video signals are transmitted. Linesbearing no information are merely scanned rapidly once. In this way adocument can be scanned many times more rapidly than as usual where allareas of the document are scanned at normal speeds compatible with thetransmission medium being employed, i.e., a telephone circuit. It willbe appreciated that when scanning printed matter and particularlytypewritten letters and the like, the majority of the scan lines willtraverse only blank paper.

In a typical facsimile transceiver corresponding to the illustratedembodiment, the vertical resolution will be on the order of 100 scanlines per inch and the horizontal resolution, along the scan lines, willbe approximately the same. This level of resolution is generallyaccepted as be ing adequate for transmitting printing, typing,handwriting, drawings and the like without loss of information and withan aesthetically acceptable level of quality. Increasing the resolutionincreases the quality of reproduced images but also increases the timerequired to transmit a document. It has been found, on the other hand,that skipping alternate scan lines, while maintaining horizontalresolution unaltered, halves the time required to transmit a documentand provides intelligible, if less pleasing, facsimile copies where theoriginal subject matter is in the nature of printing or typing. Meansare provided to accomplish this result solely at the discretion of thetransmitter operator by including switch 421, gate 412 and inverter 413.With switch 421 open the circuit of FIGURE 9 operates as previouslydescribed. In particular, at the end of a slow scan flip-flop 414 is setto permit a single advance clock pulse D at the 0 degree position to betransmitted and to actuate stepping motor 178. Immediately after thispulse has been transmitted the D F signal passes through gate 411,resets flip-flop 414, and prevents the next D signal from passingthrough gate 418. With switch 421 closed, however, inverter 413 isconnected with gate 411 and the two together function as a four inputNAND gate. Now, the 30-cycle square wave, signal H, is inverted in gate412 and applied to inverter 413 and prevents the reset signal from beingapplied to flip-flop 414 during the critical period from 18 to 36 ofrotation of drum 122. This is the period in which the second D pulseappears. Accordingly, in this mode of operation two consecutive advancepulses are transmitted and also ap lied to stepping motor 178 beforeprevideo signal G is transmitted. A typical transmitted waveform in thismode of operation is shown in FIGURE 10 Thus, a document receives twoincremental advances between each slow scan.

The double skipping feature is valuable as described but may causenarrow horizontal lines or the like to be completely missed when thetransmitter is operating in this double skipping mode. The reference tonarrow horizontal lines is intended to cover those markings which wouldbe detected along only a single scan line. With the transceiveroperating in the fast skipping mode as shown in FIGURE 10b, detection ofinformation will cause the flip-flop 414 to be reset almost immediatelyand prevent further transmission of advance clock signals D,

, as shown in FIGURE 100. With switch 421 closed, however, there wouldordinarily be a 50% probability that the signal i would be at the wronglevel and thus delay the resetting of flip-flop 414 and permitting thetransmission of one additional advance clock signal D. The ensuing slowscan would therefore not be of the line in which the information wasdetected but instead the next subsequent line. This situation issubstantially prevented by connecting the signal T to the other terminalof gate 412, which is conveniently considered as a NOR gate. When doubleskipping from one black containing line to another the circuit worksexactly as previously described, I being at the 0 volt level in therelevant time interval. However,

13 when information is first detected within a sequence of fast scans, Twill be at the minus 6 volt level, and I) T will be enabled to resetadvance control flip-flop 414 regardless of the 'state of signal fi,thus preventing the transmission of further advance signals D.

FIGURE 11 is a simplified schematic diagram of the photomultiplieramplifier 321. An inverting voltage amplifier 501 amplifies thephotomultiplier output and provides a signal which is more positive whenthe photomultiplier loo-ks at a white or background area and morenegative when it looks at a black area. This output signal is coupled toground through capacitor 502 and rectifier 503 which together functionas a peak rectifier providing an output voltage clamped to zero volts inbackground areas and negative in black areas. This voltage is coupled byresistors 505 and 506 to the normally positively biased base of pnptransistor 507. When the photomultiplier looks at a black a reaamplifier 501 will produce a negative output signal which, will causetransistor 507 to conduct and develop a output from limitingpost-amplifier 508. At other times the output of amplifier 508 islimited to minus 6- volts. During the time that photomultiplier 186would otherwise be looking at the edges of a document or other portionswhich are not transmitted, transistor 504 is gated off by signal I as aresult of which capacitor 502 is not further charged but holds itscharge in accordance with the time constant determined by its value andthat of resistors 505 and 506, i.e., remembers the background level.Accordingly, the output from amplifier 321 is a signal which is reliablyat the preselected logical 1 value when black is being scanned andlogical 0 when white is being scanned. It will be realized that morecomplex black/white decision making circuitry may also be employed suchas that disclosed in copending applications Ser. No. 329,640, filed Dec.11, 1963, or Ser. No. 461,693, filed June 7, 1965.

Receiver and alarm circuits FIGURE 12 shows the power and controlcircuits of the printer portion of the transceiver. Recording drum 122is driven by a motor 150 as already shown in FIG- URE 3. Motor 150 isoperated by signal A from FIG- URE 6, after suitable amplification by apower amplifier 601. Pen carriage 154 is mounted on a lead screw 159driven by stepping motors 160 and 161 as also shown in FIGURE 3. In thisfigure, the individual drive coils 606 for motor 160 and 607 for motor161 are shown. The stepping motors used to incrementally drive leadscrew 159 may be of any suitable type as disclosed in connection withstepping motor 178. In the described embodiment stepping motors 160 and161 may be of the Cyclo nome type manufactured by Sigma Instruments, aspreviously described in connection with stepping motor 178. A unitaryassembly of two of these uni-directional stepping motors mountedback-to-back on a common shaft is available under the designation model9AH. The stepping motors are driven by pulses applied in alternation tothe two drive coils and a special amplifier 608, shown in greater detailin FIGURE 14, is provided to generate the necessary drive pulses. Theoutput of this amplifier is connected to contacts b and c of relay K1(FIGURE 8) which direct the pulses to either the recorder steppingmotors of FIGURE 12 or the transmitter stepping motor of FIG- URE 8.When a document is not being transmitted relay K1 will not be energizedand the contacts will be in the illustrated position wherein amplifier608 is connected to the printing components rather than the transmittingcomponents.

A further set of relay contacts K3d and K3e determine whether the pulsesare applied to forward stepping motor 160 or reverse stepping motor 161.Relay K3 is illustrated in this figure and will be described. Tocomplete the description of this portion of the figure, it is noted thata further contact on relay K3 enables amplifier 608 to be driven eitherby the D pulses from FIGURE 6 or by pulses from a NOR gate 609 which isconnected both to gate 420 of FIGURE 9 and to gates 734 and 735 of FIG-URE 15, yet to be described. The pulses derived from FIGURE 9 areintended to be applied to steppin'g motor 178 of FIGURE 8 and this isaccomplished through previously described relay contacts Klb and Klcwhich switch the output of amplifier 608. The pulses from the circuit ofFIGURE 15 are the pulses intended to operate stepping motor and willpass from amplifier 608 to motor 160 through the previously describedrelay contacts when a document is not being transmitted.

A power amplifier 610 amplifies the printing or video signal from FIGURE15 and applies it to the marking tip 156 and an amplifier 611 amplifiesthe pen engage signal from FIGURE 15 and applies it to theelectromagnetic assembly 157 of pen carriage 154.

Cams 162 and 163 are associated with drum 122 as previously shown inFIGURE 3. A voltage of minus 6 volts is applied through switch 164 togrounded resistor 602, and through switch 165 to grounded resistor 604,the switches being actuated by cams 162 and 163 respectively. Thevoltage appearing directly across resistor 602 is the previouslydescribed control voltage M and this voltage when inverted in inverter603 is control voltage M. Similan'ly, the voltage across resistor 604 isinverted in inverter 605 and becomes control voltage S. These voltagesare used to control the timing circuits of FIG- URE 6 and theirfunctions have already been described. It will be understood that thereare many other ways of deriving such control voltages from the rotationof drum 122. Magnetic proximity switches, photoelectric detectors andthe like could be used equally as well as the illustrated cam operatedswitches. Furthermore, a switch or the like may be used to initiate acontrol signal at a desired position of drum 122 and a multivibratorcircuit or the like may then be used to determine the duration of thesignal. It will also be understood that the functions of switches 164and 165 may be performed through the use of additional dividing stages,gating circuits and the like in FIGURE 6. However, the illustratedmethod of deriving these signals is particularly simple, economical, andreliable.

Limit switches 612 and 613 are positioned adjacent the ends of leadscrew 159 and are adatped to be engaged by pen carriage 154 at the leftand right limits of travel. Switch 613 has a normally open contact whichis closed by contact with the pen carriage at the end of the normaltravel of carriage 154 and switch 612 has a normally closed contactwhich is opened by the pen carriage as it returns to the startingposition. The closing of switch 613 energizes relay K3 which causescontact a to close and maintain relay K3 energized through a circuitincluding switch 612. The energization of relay K3 causes the input ofdrive amplifier 608 to be connected to D signals from FIGURE 6 andcauses the output of the driver amplifier to be transferred from forwardstepping motor to reverse stepping motor 161. A further contact on relayK3 causes a control voltage to be sent to the circuit of FIGURE 15, yetto be described. With relay K3 energized, pen carriage 154 is returnedrapidly to the left at the rate of 60 increments per second by steppingmotor 161. When carriage 154 returns to the starting position, it opensswitch 612 which deenergizes relay K3 and returns the various steppingmotor drive connections to their normal forward position, preparatory torecording a new document on drum 122.

Three one-shot multivibrators 620, 621 and 622 are connected with theiroutputs in parallel so that any one of them may energize a relay K5.Multivibrator 621 is further provided with an inverter 623 to permitactuation by an incoming negative instead of positive signal. When K5 isenergized, contact a closes and maintains the relay energized through acircuit including alarm reset switch 130. The other contact b applies avoltage to a warning alarm signal 624 and to previously described alarmoscil-

1. A DRIVE CIRCUIT FOR A STEPPING MOTOR WITH FIRST AND SECOND DRIVECOILS RESPONSIVE TO ALTERNATE PULSES OF OPPOSITE POLARITY APPLIED TOSAID COILS COMPRISING: A TRIGGER FLIP-FLOP, A PUSH-PULL DRIVERAMPLIFIER, MEANS FOR COUPLING THE OUTPUT OF SAID DRIVER AMPLIFIER ACROSSSAID COILS OF SAID MOTOR. TRANSFORMER MEANS FOR COUPLING THE OUTPUT OFSAID FLIP-FLOP TO THE INPUT OF SAID DRIVER AMPLIFIER WHEREBY EACHTRANSITION OF SAID FLIP-FLOP MOMENTARILY ENERGIZES A DIFFERENT SECTIONOF SAID PUSH-PULL DRIVER AMPLIFIER THEREBY ALTERNATELY DELIVERINGCONTROLLING CURRENT TO A DIFFERENT ONE OF SAID COILS, AND DIRECT CURRENTPATH MEANS FOR INDIVIDUALLY COUPLING THE OUTPUT TERMINALS OF SAIDFLIP-FLOP TO A RESPECTIVE ONE OF SAID INPUTS OF SAID DRIVER AMPLIFIERWHEREBY